This invention relates to an automated assay instrument and, more particularly, to an assembly for blocking a port in a wall of an incubator.
Various types of chemical tests are performed by automated test equipment, an example of testing of considerable interest being the assay of biological substances for human health care. Automated test equipment allows large numbers of test samples to be processed rapidly. Such equipment is employed in health care institutions including hospitals and laboratories. Biological fluids, such as whole blood, plasma, or serum may be tested to find evidence of disease, and to monitor therapeutic drug levels, by way of example. In the automated test instrument, samples of test fluids typically are provided in sample cups, and all of the process steps including pipetting of the sample onto an assay test element, incubation and readout of a test-result signal are performed automatically. The test instrument typically includes a series of work stations each of which performs a specific step in the test procedure. The assay element or cartridge is transported from one work station to the next by means of a conveyor, such as a carousel, to enable the test steps to be accomplished sequentially. The conveyor usually carries a plurality of the assay cartridges, each secured to a specific location on the upper surface of the conveyor. In the usual arrangement, the assay cartridges are spaced apart from each other in berths which are located along the periphery of the conveyor to facilitate automatic insertion and extraction.
In many automated instruments, a pipette head assembly is utilized in combination with disposable pipette tips which are used typically only once, and then discarded so as to eliminate a possible source of contamination of fluids, thereby to prevent errors in the assay results. In such systems, the pipette head assembly is required to pick up a disposable pipette tip, aspirate the appropriate fluid into the pipette tip, such as a sample fluid from a sample cup, and to dispense the required volume of fluid to the assay element. The fluid dispensing system in such instruments must meet various requirements which will be understood better from the following description of the typical manner in which a fluid dispensing assembly operates in an automated instrument.
In a typical construction of an automated instrument, the disposable pipette tips and the sample cups are arranged on carriers which are then placed on a carrier or tray supported by a movable table within the instrument. In one type of instrument, the pipette head assembly is transported horizontally (the X) direction and vertically (the Z direction), and the trays which hold the pipette tips and the sample cups are displaced from the front to the back of the instrument (the Y direction). The conveyor can be in the form of a carousel which carries the assay cartridges with rotational movement within an incubator. Initially, the pipette head assembly is driven downwardly to secure a disposable tip by frictional contact of a stem of the pipette head assembly with the interior of the disposable tip. Thereafter, a predetermined amount of fluid is aspirated into the pipette tip, and the tip is driven to a dispense position above an assay element where a predetermined volume of fluid is dispensed. Upon completion of the dispense step, the tip is discarded and a clean disposable tip secured to the stem of the pipette head assembly for the next dispense step.
One area of concern in the accurate conduction of automated assays is the maintenance of a carefully controlled temperature in the environment of the testing. Therefore, the assay cartridges are conveyed by a suitable conveyor, such as a rotating carousel, within a temperature controlled chamber such as an incubator. The chamber includes heaters which are controlled by automatic circuitry including sensors of the chamber temperature to maintain the predesignated temperature. Indeed, it is particularly advantageous to maintain both constancy of temperature and uniformity of temperature throughout the chamber. Such temperature control can be accomplished best if the chamber is completely sealed so as to prevent the development of currents of air flowing between the environment external to the chamber and the environment within the chamber.
A problem arises in that, in one construction of the temperature-controlled chamber an access port in the form of an elongated slot is placed in a top wall or roof of the chamber to permit insertion of a pipette for transference of liquid reagents between liquid-storage sites outside the chamber and a well within the cartridge, as well as for transference of liquid between a reservoir within the cartridge and a well in the cartridge. Furthermore, a port is provided in a sidewall of the chamber to enable a cartridge injector to insert assay cartridges onto the conveyor and to extract the cartridges when the assay is completed.
Both of these ports are generally open. The elongated slot in the top wall has a minimum width since only the pipette stem and the pipette tip have to pass through it. Thus, flow of air through this slot between the inside and the outside of the chamber is substantially impeded. The port in the sidewall for inserting and extracting the assay cartridges has considerably larger dimensions to accommodate the assay cartridges as well as the load-unload mechanism. Accordingly, it can permit sufficient air to flow between the inside and the outside of the chamber to cause undesirable variations in the chamber temperature. Therefore it would be desirable to have an assembly for blocking the port when assay cartridges are not being inserted into or extracted from the incubator.